In more Prior Art researched for a rotary end cutting tool or more commonly named twist-drill bit, twist-drill, drill bit, drill and end-mill. A broad variety of concepts and theories have been availed, with some being practical, but still possessing major problems within a drill design.
A drill 30 as seen in FIG. 1, consists primarily of a shank-end (not shown), that attaches to a power unit for rotational work, and a cylindrically long body 31. In which a plural number of helical flutes 32 of geometrical design are symmetrically machined therein beginning and extending from a shank-end running parallel to an axial center-line (now shown) throughout its length towards a conical forward-end. Comprising of a like number of geometrical lands or cutting-planes 37 formed between flutes 32 and confined between a peripheral edge of body 31 that conclude at an axis-point 35. A cutting-edge 38 is then formed at a meeting of a leading plainer wall or lead-face wall 33 of each flute 32, when body 31 is rotated in a direction of R. A chisel-point system 36 is formed at and through axis-point 35 by the adjoining divisional edge-line of each cutting-plane 37. Cutting-plane 37 being set at a negative cutting or rake-angle RA (not shown), in a direction away from cutting-edge 38, which relieves a trailing-portion of face and edge of cutting-plane 37. This creates a positive cutting or shearing feed-angle, to form a hole or slot, when employed in a work-piece material in design direction R.
Further examination of Prior Art revealed many conceptions of variable designs relative to: the number, shape, angle, and area; of a helical flute 32; chisel-point system 36; cutting-plane 37; and cutting-edge 38. Some concepts may posses greater advantages and are presently being practiced. While other concepts may be too costly to produce or maintain for their advantages if any.
The primary object of a rotary end cutting tool is to produce a precise dimensional hole or slot, or a predetermined size, that is controlled by a radial length of a cutting-edge. The precision thereof; being regulated by the centering stability of these cutting-edges revolving around and axis-point.
All Prior Art researched failed to resolve the main problems that currently inhibit the efficiency of rotary end cutting tools, and more specifically, in the larger diameter drills.
After many hours of research, testing, and observation it is my opinion, that until my present invention, the two main pernicious phenomena that inhabit a rotary end cutting tool or drill have yet to be rectified. I refer to a first phenomenon as Compound Leverage Resistance (CLR), and a second phenomenon as Side Slip Differential (SSD). I consider these two names appropriate to best describing these problems. In the forthcoming description a helical drill with a drill-end design as seen in FIG. 1 will be my reference subject.
1P. Compound Leverage Resistance (CLR) pertains more to work-piece materials as opposed to drills themselves; however, drill designs do have a direct influence on the magnitude of this phenomenon. A work-piece normally has a uniform and consistent density throughout its mass. For ease of description; I will divide this means into a compact grid-pattern using a scale of 0.0254 mm (0.001 inch)=1 square, and then naming each square a unit-of-mass with a cutting resistance value of 1r. This would demonstrate a cutting-edge 6.35 mm (0.250 inch) long would experience a cutting resistance of 250r; a 12.7 mm (0.500 inch) long would grow to 500r, and so on (these values are only an example, and not a fact).
Therefore, it is my conclusion, when a rotating drill begins to penetrate a work-piece it experiences this set resistance to cutting or shearing from these units. Beginning from the initial point of contact, and remaining throughout a drilling process. This CLR phenomenon begins to evolve as the conical-end of a drill begins to penetrate. As a contacting cutting-edge progressively grows in radial-length from penetration; these units of cutting-resistance compound rapidly. Starting right from the axis-point, and extending across the cutting-edge to a point of peripheral-contact within a work-piece.
This compounded resistance being directly applied against the integral-strength of a helical-drill-body until it overcomes a designed helix-angle. Causing the cutting-edge to momentarily lag or seize until a compounding torsional-strength, through continued rotation, overcomes this CLR resistance. As a result, the cutting-edge tears free in a spring-ahead effect, in the same direction of rotation, from this accumulated torsional-force. Resulting in the cutting-edge gouging into the work-piece at a greater advanced axial-swing location, wherein the foregoing process repeats itself, and is commonly referred to as drill-chatter or flutter.
This phenomenon exists throughout a drilling process. With the drill becoming more stable after the full conical-end, and side reamers on the drill body penetrate into a work-piece. Wherein the CLR resistance to the cutting-edge and helical-body becomes more constant; which tends to stabilize and smooth out a chattering effect.
The CLR phenomenon defined; is the cutting-resistance of a unit-of-mass multiplied by its increased radial-length, and compounded to and with the next unit-of-mass in a progressive manner. This being a collective and compounding resistance against a cutting-edge; from the axis-point to a peripheral end of a cutting-edge. Although the CLR is a linear-compounding resistance phenomenon, inherent to a rotary end cutting tool, and cannot be eliminated. It can however, be reduced or better controlled by locating the origin of a cutting-edge on or behind a straight setup-line laying between the axis-point and a peripheral-edge of the body, labeled True Radius Line (TRL).
From all Prior Art researched not one demonstrated this design; but located the origin of a cutting-edge in advance of the TRL line as illustrated in FIG. 1 thru 6. This generates a Premature side-slip or Slicing motion-of-force, extending outward along a cutting-edge towards the peripheral-arc, and thereby compounding to the CLR problem; along with the SSD phenomenon that is disclosed in the next definition.
2P. The Side Slip Differential (SSD) problem is, in my opinion, the most pernicious impairment to a rotary end cutting tool; especially in larger diameters. Side Slip is derived from the progressive dimensional-arc-growth of a linear-edge traveling around an axial-center. Starting from its axis-point with the resulting surface-speed change and distance thereof differentiated in 1 degree of rotation. By taking the circumference of one 360 degree radial-arc of a given length, using this formula (2R.pi..dbd.C), and dividing this sum by the 360 degrees in one rotation, using this formula (C.div.360), you have the distance traveled per degree of rotation. Using the same formulas and procedure on a shorter radial-arc gives an answer of less value. Then subtracting this smaller sum from the first larger answer results in a difference between the two; which represents side-slip generated in one degree of radial travel; thus Side Slip Differential (SSD).
For example: "A 31.75 mm (1.25 inch) diameter Prior Art drill as seen in FIG. 14, has a 100.76 mm (3.927 inch) circumference. When divided by ONE 360 degree rotation, a distance traveled-per-degree of rotation at the periphery is 0.2769 mm (0.0109 inches). A split chisel-point consisting of 15 percent of a diameter, or a 2.38 mm (0.9375 inch) radius, calculated out; shows 0.0406 mm (0.0016 inch) distance traveled-per-degree of rotation at its peripheral-edge. Subtracting 0.0406 mm (0.0016 inch) from 0.2769 mm (0.0109 inch); would indicate a side-slip of 0.2362 mm (0.0093 inch) per degree of rotation; or a side slip distance, between the two, near equal to the peripheral-edge traveled distance."
Then adding this ordinary side-slip to or with a radial directed shear-force from rotation, combines to a compound-direction. Producing an "eddie-force" or circular-type cutting-force to the contact-point within the material. The density being a solid mass-of-unity is more resistance to shearing in a rolling or twisting fashion, (this also applies to Premature Slicing mentioned above). Thereby compounding to cutting-resistance that tends to amplify or add to both CLR and SSD problems. The Premature Slicing, mentioned in the CLR problem, tends to combine with and accelerate ordinary side-slip. With the origin of the cutting-edge being dimensionally advanced to the TRL line, (the area near the chisel-point), tends to variably-accelerate this slicing-force compounding with the SSD problem. This Premature Slicing or "eddie-force" could also be considered a Third problem to Prior Art drills. These combined phenomenons take place in every fractional dimensional-charge across a length of a cutting-edge in all Prior Art researched.
Attempts to control drill-chatter caused from the combined CLR and SSD problems using a Prior Art drill required decreasing the rake-angle RA on the cutting-plane and/or applying extreme penetrating pressure to the drill. The latter method requiring added rotational power and energy costs; while producing excessive heat. Resulting in premature dulling, chipping, or breakage to the drill; and decreased production time while sharpening or replacing thereof. Although these two (or three) phenomena are closely related, and might be considered as one problem, they are quite different. The CLR problem pertains to a multiplying-resistance to shearing that compounds against a cutting-edge rotating around an axis-point. The SSD problem pertains to the variable surface-speed difference between any two or more points of the radial-length across a cutting-edge rotating around an axis-point.
Accordingly, a minimal number of a variety of Prior Art drill-end designs, from many researched, is illustrated in FIG. 1 thru 6. In which FIG. 1 being the most common drill-end (unknown patent), with exception to flute 32 geometry, currently produced today. Wherein the centering portion being a chisel-point system 36; after finish-grinding a rake-angle RA (not shown) to each cutting-plane 37; is left with a negative cutting-angle. At a divisional line-edge of each cutting-plane 37 adjoining through axis-point 35 in regard to designed rotation R. This design, compounded by a broad residual core-area 50 thickness or diameter, allows little or no self-centering effect to occur. Moreover, this design usually requires a pilot-hole or indented-center in the work-piece, extreme pressure, and friction for penetration. Due to its negative cutting-angle feature; the chisel-point system 36 displaces or smears the material away from its path; causing difficult penetration, excessive heat, orbiting or wandering, and short drill-life. This is compounded further by cutting-edge 38 originating in advance of the TRL line; creating a Premature Slicing action that tends to push the chisel-point system 36 opposite of rotation R. Resulting in an orbital-vibration or flutter. With further penetration of the conical-end into a work-piece; the CLR and SSD problems start to take effect. Causing the drill 30 to intensify vibration and chatter in an orbital-manner until the side-cutters 46 immerse into the work-piece; and then begins to reasonably stabilize. This design can be very destructive to both drill and/or work-piece in some materials; which has inspired many new concepts attempting to rectify this problem.
FIG. 2 is a drill-end illustration of U.S. Pat. No. 4,381,162, R. Hoise, dated Apr. 26, 1983. Wherein cemented cutting-planes 37, cutting-edges 38, chisel-point system 36, and side-cutters 46 are fused into body 31 as a unit. It also possesses a thicker residual core-area 50 than seen in FIG. 1; for improved integral-strength therein. Improvements to chisel-point system 36 being split, and radiused into cutting-edge 38; tends to increase the overall length of cutting-edge 38, and projects the original of cutting-edge 38 in a greater advance of the TRL line. In my opinion; this would amplify the SSD problem, especially in larger diameters; and would tend to require greater torsional-power to rotate in a work-piece as compared to the drill in FIG. 1. Chisel-point system 36 may have fair to good centering and penetration capabilities upon initial contact however, it does not rectify the CLR and SSD problems, and appears to add to the Premature Slicing problem as well.
FIG. 3 is a drill-end illustration of U.S. Pat. No. 4,556,347, H. Barish, dated Dec. 3, 1985. Wherein the residual core-area 50 is of greater thickness and similar to FIG. 2. Having a split chisel-point system 36 provided from an extreme negative-angled plane added to the rake-angle RA (not shown) on a rear-portion of each cutting-plane 37; and cutting-edge 38 contains a dihedral-angled edge. This probably improves the centering and penetration qualities; but, still places cutting-edge 38 in advance of the TRL line. The increased length and location of cutting-edge 38 would indicate that greater torsional-power is required, as opposed to the drill in FIG. 1, and could add to both CLR and SSD problems. Test data contained in this patent reflects that drill diameters used were less than 6.35 mm (0.250 inches) with no reference provided to larger diameters being tested.
FIG. 4 is a drill-end illustration of U.S. Pat. No. 5,088,863, K. Imanaga, S. Nakamura, H. Hosono, Y. Yanase, dated Feb. 18, 1992. Wherein the residual core-area 50, and flue 32 geometry can possess a number of variables. The trailing portion of cutting-plane 37 being back-cut on a strong negative-angle; to establish the split chisel-point system 36 similar to FIG. 3. With the entire drill (not shown) being coated with one from a variety of variable metal-alloys depicted. It probably has good centering and penetrating capabilities in the chisel-point system 36 area. However, cutting-edges 38 originate in advance of the TRL line with little or no resolution to either CLR or SSD problems as well. Some concern is also directed to rotational-stability in thin work-piece materials. Test data contained in this patent implies that the largest diameter drill used was 12.5 mm (0.492 inch); which is, more-or-less, near the point where both the CLR and SSD problems start to become very apparent.
FIG. 5 is a drill-end illustration of U.S. Pat. No. 4,950,108, A. Ross, dated Aug. 21, 1990, wherein the entire conical cutting-end 60 is a replaceable unit. Fixed to the forward-end of body 31 by counter-sunk sleeves 61, and cap-screws 62; which is aligned on body 31 by an individual center-dowel 63. This chisel-point system 36, similar to FIG. 3 and 4, is split; but, like FIG. 2 is radiused into the cutting-edge 38 far in advance of the TRL line; and is all contained in a unit-embodiment. Body 31 also contains split flushing-ports 64 in which each port angles in towards and connects to a central void or channel (not shown). That is contained in and through residual core-area 50; which terminates near the shank-end (not shown). This design appears to display the same negative disadvantages to the CLR and SSD problems as modes FIG. 2. The design of this replaceable cutting-end 60 appears to be limited in regard to minimal drill 30 diameters; and cumbersome to change while mounted in a vertical power-head. This method of fixing the cutting-end 60 to the body 31 warrants some concern to the integral-strength of this type of mounting; as well as in regards to the helix-angle used (not shown).
FIG. 6 is a drill-end illustration of U.S. Pat. No. 5,011,342, G. Hsu, dated Apr. 30, 1991. Wherein the chisel-point system 36 being similar to those seen in FIG. 3 and 4 is split; but, at different face-angles from each other. Each cutting-plane 37 has a single groove 41 of specific dimensions and shape, being fixed on the same radial-center, on either cutting-plane 37. This split chisel-point system 36 should afford adequate centering and penetration capabilities. However, similar to FIG. 3 and 4, the intersecting point of cutting-edge 38 and chisel-point system 36 will experience compounded pressures from two directions; which tend to cause premature failure. The origin of cutting-edge 38 being in advance of the TRL line also appears to increase or magnify the Premature Slicing problem as well as CLR and SSD problems. This single groove 41 on each cutting-plane 37, being incorporated into cutting-edge 38, initially would tend to stabilize the SSD problem in a work-piece. But, after both grooves 41 are completely immersed and tracking each other would tend to add length to cutting-edge 38 producing added resistance; requiring more rotational power over initial contact with the work-piece. Consequently, the CLR and SSD problems are not rectified.
Although the aforementioned patents, among others researched, with their theories and concepts are felt to be of interest; they are not considered to be relevant.